<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>边框</title>
    <style>
        /* border：1px sold gray */
        .box1 {
            width: 100px;
            height: 100px;
            background: yellow;
            border: 10px dotted red;

            /* 样式：solid实体线 double双线 dashed虚线 dotted单点线 */
            /* 背景色 也能蔓延到边框 */
        }
        .box2{
            width: 100px;
            height: 100px;
            background: blue;
            border-top:5px solid red;
            border-left:5px dashed yellow;
        }
        .box3{
            width: 100px;
            height: 100px;
            background: green;
            border-width: 10px 20px 30px 40px;
            border-color:yellow blue black red;
            border-style: solid double dashed dotted;
            /* 
            border

            border-width 
            border-style
            border-color 
            */
           
        }
    </style>
</head>

<body>
    <div class="box1">

    </div>
    <div class="box2">

    </div>
    <div class="box3">

    </div>
</body>

</html>